The regulatory subunit of the cAMP-dependent protein kinase appears to have distinct domains that function in (1) dimerization, (2) binding and inhibition of the catalytic subunit and (3) binding of cAMP. Recombinant DNA techniques will be used to prepare truncated versions of the regulatory subunit lacking one or more of the functional domains listed above. These experiments will utilize cDNA clones. Mutants will be constructed by deletion and by site directed mutagenesis. These mutant cDNAs will be incorporated into eucaryotic expression vectors containing the Zn++ inducible metallothionein promoter. These vectors will be used to transfect Y1 adrenal cells in culture so that the truncated proteins can be expressed, isolated and characterized.